Molded resin articles have been decorated in the past with graphic and/or indicia patterns (such as letters, figures, symbols and the like) using known foil-decorating techniques. According to the foil-decorating technique, a molded surface-patterned article is prepared by placing in a mold cavity a resin film bearing a selected graphic and/or indicia pattern, filling the mold cavity with a molten resin (or a resin prepolymer) and then compressing the thus obtained molded article under heat and pressure to integrate the film onto a surface of the molded article. In the case of thermosetting resins, this heat and pressure treatment serves to cause the resin to react further.
The foil-decorating technique has been used extensively to decorate the surfaces of molded articles formed of thermosetting resins (e.g. melamine resin) with pictorial patterns. However, when thermosetting resins are used to form surface-patterned articles, the steps employed in foil-decorating become relatively complex thereby increasing the costs associated with manufacturing such articles. Accordingly, the use of foil-decorating techniques using thermoplastic resins has recently gained more attention because molded articles of thermoplastic resins are more easily obtained by injection molding techniques, resulting in lower production costs. In this regard, foil-decorated injection-molded articles using polyolefins, such as polypropylene have been commercialized.
The thermoplastic polyolefin resins that have typically been used in foil-decorating techniques generally exhibit poor heat resistance, strength and rigidity. Thus, although these typical resins can be used to form injection-molded articles that may be employed in some end-use applications, they cannot usually be employed in end-use applications where severe conditions may be encountered. In the case of injection-molded tableware, food vessels or trays, for example, a number of additional performance requirements must be met. Specifically, the odor and/or color of food must not migrate into the resin. Conversely the odor and/or "taste" of the resin should not migrate into the food.
Molded articles satisfying all of the foregoing requirements have not been developed to date. It is therefore towards fulfilling such a need that the present invention is directed.
The present invention broadly resides in foil-decorated surface-patterned articles whereby a back-printed film of a polyester resin is adhered to a surface region of a body comprised of a different PBT resin. In this regard, PBT resins have not been used previously as a substrate body for foil-decorations.
More specifically, in accordance with the present invention, a process for preparing a surface-decorated polybutylene terephthalate resin molded article (i.e., having a graphic and/or indicia pattern formed on a surface of the article) is especially characterized by placing a film composed mainly of a polyester (preferably polybutylene terephthalate) resin having a melting point which is 10.degree. C. to 60.degree. C. less than the melting point of the PBT resin forming the article's body, and back-printed with the desired pattern, in a cavity of a mold so that the printed surface of the film will be in contact with the subsequently injected PBT body resin. Molten PBT resin comprised of polybutylene terephthalate is then injected into the mold cavity to fill the same and to cause the polyester film to at least partially plasticize. As a result, the polyester film integrally coalesces (bonds) onto a surface portion of the molded PBT resin article. The resulting equally novel molded article prepared according to this process will thereby have a surface which corresponds to the film, and will exhibit the pattern associated with that film.